Print media used in inkjet printing are typically categorized into two groups: porous media and swellable media, with each of the groups having particular advantages and disadvantages. For instance, porous media have an ink-receiving layer that is formed from inorganic or organic materials, such as porous, inorganic particles or porous, organic particles. The porous particles are bound with a binder. The inorganic particles are typically silica- or aluminum-based compounds, such as silicon oxides or aluminum oxides, while organic polymers, such as polyvinylpyrrolidone, are used in the organic particles. When inkjet ink is applied to a porous medium, the inkjet ink is absorbed into the pores of the particles. A colorant in the inkjet ink is fixed in the porous medium by mordants incorporated in the ink-receiving layer or by the surface of the inorganic or organic particles. Porous media have a short dry time and good resistance to smearing because the inkjet ink is easily absorbed into the pores of the ink-receiving layer. However, porous media do not have good resistance to airfade or good lightfastness. In addition, porous media that use organic particles can have poor gloss. In swellable media, the ink-receiving layer is a continuous layer of a swellable, polymer matrix. The polymer used in the swellable matrix is typically water-soluble or swellable, such as polyvinyl alcohol (“PVA”), polyvinylpyrrolidone (“PVP”), or gelatin. When the inkjet ink is applied to the swellable medium, the inkjet ink is absorbed by swelling of the polymer matrix and the colorant is immobilized inside the continuous layer. Since the colorant is protected from the outside environment, swellable media have greater resistance to light and dark/air fade and better color gamut than the porous media. However, the swellable media generally have reduced smearfastness and a longer drytime than porous media.
PVA or PVP is a component of many porous media. For instance, PVA or PVP is typically used in small amounts as the binder in the porous media. The PVA or PVP bind together the inorganic or organic materials, which are present in the porous medium to absorb the inkjet ink. PVA is an inexpensive, commercially available material and has been formed by many techniques, such as by an alcoholysis reaction of polyvinylacetate (“PVAc”) with a basic catalyst.
PVA has also been used as a packing material in gel chromatography. When used as a packing material, the PVA is commonly crosslinked. Crosslinked PVA has been produced by a variety of techniques, such as by reacting PVA with a crosslinking agent; suspending a mixture of PVAc, an organic solvent, and a diluent in a nonsolvent and crosslinking the particles; and suspension polymerizing PVAc with a crosslinking agent and a diluent. However, these techniques produce crosslinked PVA in a gel form or produce particles of crosslinked PVA that have a large particle size, such as a particle size of 10 μm-1000 μm. The large particle size is necessary to provide sufficient capacity to separate compounds that are passed through a column of the crosslinked PVA particles. However, this large particle size is not desirably used in inkjet print media because the color density of the resulting print medium is lower compared to that of a swellable medium.
Another problem with these techniques of forming crosslinked PVA is that the crosslinking agents are susceptible to hydrolysis when exposed to alkali or basic conditions. The alkali conditions used to hydrolyze the PVAc to PVA also hydrolyze the crosslinking agents. Severing the bound crosslinking agent causes the crosslinked PVA particles to disintegrate and lose their shape, forming a soft gel. Therefore, to maintain a hard, porous PVA structure, the soft gel is subjected to a post-crosslinking process, which typically uses epichlorohydrin to re-crosslink the crosslinking agents.
It would be desirable to provide porous or nonporous, crosslinked organic particles that have high porosity, fast ink absorption rate, and high color density.